In a drive device such as a stepping motor, a coil device is used which is structured of a coil member such as a coil bobbin around which a coil is wound. The coil member which is used in the coil device is commonly formed such that resin is injected into a cavity which is formed by combining a plurality of molding resin dies having a divided structure with each other together with a stator core and, after resin has been solidified, the molding resin dies are separated from each other to form the coil member. Therefore, a burr may be formed in a projected manner between jointing faces of the molding dies. When the burr is formed in a drum part around which a coil is wound, the burr and the coil may be abutted with each other to cause disconnection of the coil to occur. In order to prevent this problem, it has been disclosed that, as shown in FIG. 8, undercut parts 202 are formed on a cylindrical part 201 of a drum part 207, around which a coil is wound, along a parting line 205 which is formed by joining faces of the molding resin dies 204 and 204′ as shown in FIG. 9. According to the structure as described above, the burr 203 is formed at a concaved position from an outer peripheral face 208 for winding of the drum part 207 to prevent disconnection of the coil (see, for example, Japanese Patent Laid-Open No. 2003-347117).
As shown in FIG. 9, in the coil member disclosed in the above-mentioned Patent Reference, the undercut parts 202 aye formed by the molding resin dies 204 and 204′ and, after molding, the drum part 207 is released from the molding resin dies 204 and 204′. However, when the molding resin dies 204 and 204′ are separated from each other in directions shown by the arrow “P” and “P′”, protruded parts 206 and 206′ of the molding resin dies 204 and 204′ press the drum part 207. Especially in a coil member used in a small motor, a wall thickness of the drum part 207 is very thin. Therefore, when the molding resin dies 204 and 204′ are separated from each other, the drum part 207 is pressed by the protruded parts 206 and 206′ to cause a crack to occur and, in the worst case, the drum part 207 is unable to endure a winding pressure of a coil which is wound around the drum part 207 and thus the coil member is damaged.